1. The Technical Field
The present invention is directed generally to solenoid actuators and more particularly to a novel solenoid actuator having a captive armature that is especially well-suited for use as a valve actuator in liquid and gas systems.
2. The Related Art
A conventional solenoid actuator typically includes a ferrous plug attached to one end of a non-ferrous coil tube by conventional means, for example, welding, gluing, roll-forming, or crimping. Depending on the attachment method used, an O-ring may be provided to form a seal between the plug and coil tube. The other end of the coil tube is assembled to a valve body mounting plate in a manner that effects a seal between the coil tube and mounting plate. The free end of the coil tube is inserted into the inside diameter of a wound electromagnetic coil. A frame is installed to this assembly, typically by means of screws or other fasteners securing the frame to the valve body mounting plate, to secure the coil to the mounting plate. The frame typically includes a hole having an inside diameter slightly larger than the outside diameter of the coil tube through which the end of the coil tube extends.
An armature is inserted into the open end of the coil tube. Typically, a return spring is provided to bias the armature away from the plug at the opposite end of the coil tube. A valve poppet is mounted near the free end of the armature. A spring retainer and/or flat washer may be installed between the spring and valve poppet. The entire assembly then is mounted to a valve body, typically using threaded fasteners.
This conventional design has many shortcomings. First, the armature is free to fall out of the coil tube except when the actuator is assembled to the valve body. Nothing prevents the armature from falling out of the coil tube while assembling the actuator to the valve body or when removing the actuator from the valve body for maintenance, for example, replacement of the valve poppet. This makes it impractical to use automated assembly equipment for assembling the actuator to the valve body. Second, the mechanical joint and/or seal between the plug and coil tube can become compromised as a result of the armature hammering against the plug as the actuator is cycled during normal use. Third, the use of threaded fasteners to secure the frame to the valve body mounting plate adds expense and complexity to the assembly process. Fourth, such fasteners can back out during operation as a result of vibration, resulting in failure of the actuator and loss of valve function.
Another, less common, known technology uses a coil tube having a plug attached at one end, as described above, and a flange at the other end. The coil tube is inserted into a gasket, a frame, and a wound coil. This assembly is then mated to a valve body such that the gasket forms a seal between the coil tube flange and frame. Another gasket may be provided to form a seal between the foregoing assembly and the valve body. This technology suffers from all of the shortcomings described above and the additional shortcoming of a coil tube that is not secured by the frame and, therefore, must be retained by some external means until the actuator is assembled to the valve body.